1. Field of the Invention
This invention relates to polymeric coloring compositions. More particularly, it relates to water-soluble polymeric colorants, especially water-soluble polymeric colorants which are nontoxic and thus are useful in edibles and their preparation.
2. Background Art
Polymeric colorants are composed of optically chromophoric groups bound to or into polymers. Such materials may be found in the prior art, for example, in Horiguchi et al's U.S. Pat. No. 3,337,288 granted on Aug. 22, 1967; in Wegmann et al's U.S. Pat. No. 3,304,297, granted on Feb. 14, 1967; in Japanese Published Patent Application No. 14,434, published in 1966 and cited at 66 Chemical Abstracts 19843 j; in the article by Ida et al. appearing at pages 524-30 of volume 89(4) of YAKUGAKU ZASSHI; in Kalopissis's U.S. Pat. No. 3,567,678 granted on Mar. 2, 1971; and Dawson et al.'s U.S. Ser. No. 420,545, filed on Nov. 30, 1973 and now issued as U.S. Pat. No. 3,920,855 on Nov. 18, 1975. These and other references make it clear that in certain applications polymeric dyes can offer real functional advantages. Their larger molecular size reduces their diffusivity and increases their film-forming properties. In food coloring applications, polymeric colors can offer yet another advantage which is pointed out in the already noted Ida et al. and Dawson et al. references. If a polymeric color molecule has a large enough molecular weight and size, it will be too large to be absorbed from the gastrointestinal tract when eaten with food. This means that the color will not pass into the body and any risk of systemic toxicity is essentially eliminated.
In such food coloring uses and in other applications where the polymeric properties of a polymeric colorant are of importance, it is required that the chromophoric groups be stably attached to the polymer and that the polymer itself not undergo degradation under the conditions of use.
In many, if not most, applications it is desirable that the polymeric colorants be water-soluble since most substrates to be colored, especially edible substrates, contain water. One way to impart water-solubility is to incorporate water-solubilizing groups in the polymer backbone. Such an approach has the disadvantages of requiring a new backbone to be prepared each time an increase or decrease in solubility is desired and of introducing potentially liable groups into the ideally nonrupturable backbone. Another approach is imparting water-solubility is to use only chromophoric units which contain solubilizing groups -- which approach limits the choice of chromophoric units which can be employed. Yet another approach involves attaching solubilizing groups to the chromophores themselves. This generally results in undesired modification and unpredictability of the color of the final polymer product.
Probably the best and most generally applicable method to prepare a water-soluble polymeric dye is to attach water-solubilizing groups and chromophoric groups directly and separately to the polymer backbone. It is to such materials that the present invention relates.